It has long been recognized that the properties of polymers can be controlled to a high degree through variables such as morphology, composition, thermodynamics and processing conditions. It is similarly known that various sizes and shapes of fillers (e.g. calcium carbonate, silica, carbon black, rubber, etc.) can be inserted or compounded into a polymer to somewhat control both polymer morphology and the resulting physical properties.
In their solid state, all polymers (including amorphous, semi-crystalline, crystalline, rubber, etc.) possess considerable amounts of internal and external free volume (see FIG. 1). The free volume of a polymer has a tremendous impact on its physical properties, since it is within this volume that the dynamic properties (e.g. reptation, translation, rotation, crystallization) of polymer chains primarily operate and in turn influence fundamental physical properties such as density, thermal conductivity, glass transition, melt transition, modulus, relaxation, stress transfer, and surface properties.
The accessibility of free volume in a polymer system depends greatly on its morphology. As shown in FIG. 2, for example, denser regions and phase separation within a polymer can both increase and decrease the thermodynamic and kinetic access to such areas. Because of its influence on thermodynamic and kinetic properties, polymer morphology is a major factor that limits the ability of conventional fillers from accessing the free volume regions in a polymer system. Additional processing/compounding effort is normally required to force compatibilization between a filler and a polymer system because conventional fillers are physically larger than most polymer dimensions, are chemically dissimilar, and usually are high melting solids.
Prior art in compounding has focussed on incorporating polymer systems with small, low molecular weight molecules (liquids and solids) known as plasticizers or plasticizing agents and with macro, micro and nanoscale particulates of dissimilar composition (e.g. inorganic) to that of the polymer (organic). The function of a plasticizing agent is to aid in the slippage of polymer chains by one another, thus improving the processability and manufacturability of a particular polymer system. Similarly fillers, which have traditionally been composed of fibrous or particulate solids, have been combined with polymers to enhance physical properties such as dimensional stability, impact resistance, tensile and compressive strengths, and thermal stability. Unfortunately, where plasticizers are too small to reinforce polymer chains, traditional fillers are too large to reinforce individual polymer chains and segments. Fillers are traditionally utilized to macroscopically reinforce large associated or nearby groups of polymers rather than the individual chains and segments within these polymers.
It has been calculated that as filler sizes decrease below 50 nm, they become more resistant to sedimentation and are more effective at providing reinforcement to polymer systems and consequently improving control over physical properties. The full application of this theoretical knowledge, however, has been thwarted by the lack of a practical source of particulates with monodispersity and diameters below the 50 nm range and especially at or below the 10 nm range. Particularly desirable are metallic particles that are monodisperse or which have controlled and narrow particle size distributions as these are expected to form the most stable dispersions within polymer systems. In addition, these particles would be well below the length scale necessary to scatter light and hence should appear transparent when compounded into plastics.
Recent developments in nanoscience have now enabled the ability to cost effectively manufacture commercial quantities of materials that are best described as metallized nanostructured chemicals due to their specific and precise chemical formula, hybrid (inorganic-organic) chemical composition, and large physical size relative to the size of traditional chemical molecules (0.3-0.5 nm) and relative to larger sized traditional fillers (>50 nm).
Nanostructured chemicals can be based on low-cost Polyhedral Oligomeric Silsesquioxanes (POSS) and Polyhedral Oligomeric Silicates (POS). Metallized nanostructured chemicals which are also known as Polyhedral Oligomeric Metallosesquioxanes (POMS) are cages that contain one or more metals inside or outside or bonded to the cage. In certain instances cages may contain more than one metal atom, or types of metal atoms or metal alloys. POMS are illustrated by the representative structure and formula shown in FIG. 3. Note that POMS are structurally and compositionally diverse and may contain several polyhedra, polymorphs, and compositional variances that can be utilized to control the physical properties of the POMS and the materials into which they are incorporated (FIG. 4).
Like POSS cages, POMS systems contain hybrid (i.e. organic-inorganic) compositions in which the internal frameworks are primarily comprised of inorganic silicon-oxygen bonds. The exterior of a nanostructure is covered by both reactive and nonreactive organic functionalities (R), which ensure compatibility and tailorability of the nanostructure with organic polymers. These and other properties of metallized nanostructured POSS chemicals are discussed in U.S. Pat. No. 5,589,562 and by Hanssen, van Santen, and Abbenhuis, 2004 Eur. J. Inorg. Chem. 675-83, both incorporated herein by reference. Unlike metal fillers or particulate fillers, these POMS nanostructured chemicals are of low density (range 1.17 g/ml to 2.04 g/ml); highly dispersible into polymers and solvents; exhibit excellent inherent fire retardancy; optical, electronic properties, and radiation tolerance; and can range in diameter from 0.5 nm to 50 nm.
Prior art associated with fillers, plasticizers, and polymer morphology has not been able to adequately control polymer chain, coil and segmental motion, optical and electronic properties at a molecular level. Furthermore, the mismatch of chemical potential (e.g. solubility, miscibility, etc.) between hydrocarbon-based polymers and inorganic-based fillers resulted in a high level of heterogeneity in compounded polymers that is akin to oil mixed with water. Therefore, there exists a need for appropriately sized metal containing agents for polymer systems with precisely controlled diameters (nanodimensions), distributions and with tailorable chemical functionality. In addition, it would be useful to have easily compoundable metallized nanoreinforcements that have chemical potential (miscibility) ranges similar to the various polymer systems.